A fish and shellfish culture technique with recirculatory system may be found in the literature such as "Method of purifying water in fish and shellfish culture facility and device thereof" in Japanese Patent Publication KOKOKU No. 49-37679, in which carbon dioxide, one of toxic metabolic products of fish and shellfish is removed from water in a culture facility and oxygen is supplied to the water in such the ways that carbon dioxide is removed by blowing air into the water; and ammonia or inorganic materials dissolved in the water are absorbed by zeolite or activated carbon, and that oxygen-rich air is blown into the water for supplying oxygen.
There have been various methods of purifying water in a fish and/or shellfish culture. The conventional oxidative disintegration method, for example, intended to disintegrate materials dissolved in water by blowing oxygen into water, is not an effective way to remove unwanted materials because of an insufficient contact of the unwanted materials with oxygen. The absorption method, intended to absorb away unwanted materials dissolved in water using zeolite or activated carbon, has another problem in relation to its extended period of operation, because the materials of zeolite or activated carbon are susceptible to clogging, unless they are frequently replaced with fresh materials or cleaned. To remove unwanted organic and/or inorganic materials dissolved in water, especially ammonia, is the most imperative problem for maintaining water quality suitable for an aquaculture of any given species of organism.
In the conventional aquarium with recirculatory system for fish and/or shellfish culture, a culturing tank is directly connected to a water purifying facility. When an accident happens during the operation of the system, water quality can be immediately deteriorated to cause an adverse effect on the cultivated organisms, resulting frequently in the death of a majority of the organisms.
One of the objectives of the present invention is to solve aforementioned problems and to provide an aquarium with a closed water recirculatory system in which unwanted materials dissolved in water, especially ammonia, are effectively removed away from the system during an extended period of its operation and an entire aquarium system (culture facility, ibid) is arranged in such a way that an operational accident of the system does not immediately affect on water quality in the rearing tank.